Method and device for regulating fluid pump pressures

ABSTRACT

A method is provided for regulating fluid pump pressures by detecting an elevation differential between a fluid flow control device and the distal end of a fluid line in communication with the fluid flow control device. A fluid flow control device, for instance a peritoneal dialysis device, is at a first height, a distal end of a fluid line is at a second height, and a valved outlet, when open, affords communication between the fluid flow control device and the distal end of the fluid line. The elevation differential is correlatable with a pressure measurable during a calibration procedure provided as a part of the methodology.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/177,625 filed Jul. 22, 2008 and entitled Method and Device forRegulating Fluid Pump Pressures (F67), which is a divisional of U.S.application Ser. No. 10/972,982 filed Oct. 25, 2004 and entitled Methodand Device for Regulating Fluid Pump Pressures (E24), now U.S. Pat. No.7,421,316, issued Sep. 2, 2008, which is a divisional of U.S.application Ser. No. 10/320,178, filed Dec. 16, 2002 and entitled Systemfor Regulating Fluid Pump Pressures (D40), now U.S. Pat. No. 6,808,369,issued Oct. 26, 2004, which is a divisional of U.S. application Ser. No.09/612,005, filed Jul. 10, 2000 and entitled Method for Regulating FluidPump Pressures (B85), now U.S. Pat. No. 6,503,062, issued Jan. 7, 2003,which are hereby incorporated herein by reference, in their entireties.

TECHNICAL FIELD

The present invention relates to fluid flow control devices and, morespecifically, to regulating pump pressures. In particular, the inventionprovides a method and apparatus for increasing the fluid flow rate in afluid flow control device while maintaining desired pressure levels. Thepresent invention also relates to systems that can determine therelative elevation of a pump with respect to a distal end of a line incommunication with the pump.

BACKGROUND ART

A function of fluid flow control systems is to regulate the rate ofdistribution of transport fluid through a line. Some examples of fluidcontrol devices are peritoneal dialysis machines and intravenous fluiddelivery systems. Fluid flow control systems may include a permanenthousing which does not come into direct contact with the transportingfluid and into which a fluid-exposed disposable cassette is placed.Flexible membranes, or other structures that respond to pressure,maintain separation between the permanent and disposable components.Examples of such control systems and their sub-components (inparticular, valves) are disclosed in U.S. Pat. Nos. 4,778,451,4,976,162, 5,088,515, and 5,178,182. These patents are all issued toKamen and are all hereby incorporated herein by reference.

One problem with respect to fluid flow control devices arises in, forexample dialysis treatment. Patients want to minimize the time spenthooked up to the peritoneal dialysis machine. In order to satisfypatient demands, the flow rate of the fluid pumped into the patient'scatheter may be proportionally increased by increasing the pumpingpressure. However, international specifications (for example, EN 50072)regulate the maximum and minimum pressures allowed in the patient'scatheter. The maximum positive pressure allowable is set at −150 mm Hg(.about.0.3 psi), and the minimum (or maximum negative, or suctionpressure) is set at .about.75 mm Hg (.about.−1.5 psi). Prior artdialysis machines use pumping pressures of about 75 mm Hg (1.5 psi) whenpumping fluid into the patient. If the dialysis machine and the patientare at the same elevation, the pressure applied at the pump will be veryclose to the pressure at the patient's catheter. If, on the other hand,the dialysis machine is elevated above the patient, the pressure at thepatient's catheter will be higher than the pressure applied at the pump.Consequently, to insure a margin of safety, the pumping pressure is setwell below the maximum allowable pressure to compensate for anyuncertainty in the position of the patient relative to the dialysismachine.

SUMMARY OF THE INVENTION

A method is provided for regulating fluid pump pressures based on therelative elevation between a fluid flow control device and a distal endof a fluid line by providing at least one liquid volume in valvedcommunication with the distal end. The pressure measurement of theliquid volume is calibrated, and then valving is opened to establishcommunication between the liquid volume and the distal end of the fluidline. A pressure associated with the liquid volume is measured, and thefluid pump pressure is adjusted in accordance with the measuredpressure.

Preferably, the fluid flow control device has two liquid volumes. Afirst liquid volume is in valved communication with a second liquidvolume. The fluid line is preferably in valved communication with bothliquid volumes. The pressures in the liquid volumes are calibrated, andcommunication between one liquid volume and the distal end of the fluidline is established. A pressure associated with the one liquid volume ismeasured, and the fluid pump pressure is adjusted in accordance with themeasured pressure.

The fluid flow control device preferably includes a control volume foreach liquid volume, a transducer for each control volume, and aprocessor for reading and storing pressure values, computing andidentifying a correlation between pressure values, and calculatingpressure values based on identified correlations. The processor mayestimate the elevation differential based upon the pressure values,and/or regulate fluid pump pressures. The fluid flow control device mayalso include pressure means for pressurizing a liquid volume. The devicemay further include one of a wide variety of valve arrangements forcontrolling fluid communication between the liquid volumes and thedistal end of the line. The processor may also control the valvearrangement, the means for pressurizing the liquid volume, and the fluidpump pressure.

In another preferred embodiment, the liquid volume and the controlvolume themselves are parts of a pump. Preferably, the pump includes aflexible membrane that divides the liquid volume and the control volume.In other embodiments, the fluid flow control device includes a pump.

In a preferred method for detecting the relative elevation between afirst location and a second location, a fluid flow control device isprovided at the first location with at least one membrane pump in valvedcommunication with the second location. The membrane pump is isolatedfrom the second location, and a pressure transducer of the membrane pumpis calibrated. Valving is then opened to establish communication betweenthe membrane pump and the second location. The pressure of the membranepump is measured, and the relative elevation between the first locationand the second location is estimated.

In a further embodiment, calibrating the pressure transducer may includefilling the membrane pump with fluid in pressure equilibrium with thepressure at the first location, measuring a first calibration pressureof the membrane pump, filling the membrane pump with fluid in pressureequilibrium with a known (i.e., predetermined or measured) calibrationpressure, and measuring a second calibration pressure of the membranepump. The relative elevation between the first location and the secondlocation may be estimated based on the known calibration pressure, thefirst calibration pressure, and the second calibration pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a perspective view of a prior art fluid flow control device;

FIG. 2 illustrates a membrane-based fluid flow control system containedin the device of FIG. 1;

FIGS. 3( a) and 3(b) schematically illustrate the relationship betweenthe relative elevation of the fluid flow control device and the pressureexperienced at the distal end of a fluid line;

FIG. 4 is a block diagram illustrating the process of detecting therelative elevation and regulating fluid pump pressure according to oneembodiment of the present invention;

FIGS. 5( a) and 5(b) are block diagrams illustrating calibration andregulation processes according to another embodiment of the invention;and

FIG. 6 is a graphical representation of the relationship derived fromthe process of FIG. 5.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 shows a prior art fluid flow control device 200. A disposablecassette 201 is securely mounted onto the fluid flow control device 200.Fluid communication with the cassette 201 is maintained from a heatedsolution bag 202 via a solution inlet line 203 and is also maintained toa distal end 208 of an outlet line 204. The fluid flow control device200 has an occluder bar 205 that when activated by the fluid flowcontrol device 200, occludes both the inlet line 203 and the outlet line204. The fluid flow control device 200 is shown to have two pumps 300and 310, each pump having inlet and outlet valves 306, 307, 316, and317.

FIG. 2 illustrates a membrane-based fluid control flow system utilizedin fluid flow control device 200 of FIG. 1 and having a first pump 300and a second pump 310. Flexible membrane 303 is shown as dividing firstpump 300 into a first control volume 301 and a first liquid volume 302.The first control volume 301 may be pressurized through a first pressureline 304. The pressure in the first control volume 301 is measured by afirst pressure transducer 305 attached to and in fluid communicationwith the first control volume 301. Similarly, flexible membrane 313divides second pump 310 into a second control volume 311 and a secondliquid volume 312. The second control volume 311 may be pressurizedthrough a second pressure line 314. The pressure in the second controlvolume 311 is measured by a second pressure transducer 315 attached andin fluid communication with the second control volume 311. Pressurizingmay occur through the use of a control gas or liquid, or other methodsknown in the art, such as pumps, pistons, pressurized reservoirs,valves, and vents. As noted above these pressurizing devices areexplained in greater detail in the U.S. patents issued to Kamen andincorporated herein by reference.

A first outlet valve 306 controls the outlet flow from the first liquidvolume 302 to the outlet line 204 and a second outlet valve 316 controlsthe outlet flow from the second liquid volume 312 to the outlet line204. The outlet flows from the first pump 300 and second pump 310 are,therefore, in fluid communication with each other and with the distalend 208 (see FIG. 1) of the outlet line 204. A first inlet valve 307controls the inlet flow into the first liquid volume 302, and a secondinlet valve 317 controls the inlet flow into the second liquid volume312. The inlet flows from the first pump 300 and the second pump 310 arein fluid communication with each other and with the heated solution bag202 through solution inlet line 203. When activated, the occluder bar205 isolates both the outlet line 204 and the solution bag 202 from thepumps 300 and 310 while allowing fluid communication between the twopumps 300 and 310 when either or both sets of valves are open.

FIG. 3( a) schematically illustrates a fluid line 204 in communicationwith a subject 31 at the same elevation as a fluid flow control device200. When the distal end 208 of the line 204 and the fluid flow controldevice 200 are at the same elevation, the pressure at the distal end 208of the line 204 is equal to the pressure in the fluid flow controldevice 200. FIG. 3( b) schematically illustrates a subject 31 at a lowerelevation to that of fluid flow control device 200. When this situationoccurs, the pressure in the distal end 208 of the line 204 is greaterthan the pressure in the fluid flow control device 200. If, for example,the fluid flow control device 200 is a peritoneal dialysis machine, therelationship between the relative elevation and the pressuredifferential may be calculated. A 0.3 m (one foot) elevation differencebetween the patient and the dialysis machine results in about 25 mm Hg(0.5 psi) difference between the pressure in the dialysis machine andthe pressure in the catheter attached to the patient. Clearly, the lowerthe patient is in relation to the dialysis machine, the greater thepressure will be in the catheter. Therefore, for the example discussedabove, if it were possible to determine the relative elevation of thepatient with respect to the dialysis machine, the pumping pressure couldbe decreased to maintain a margin of safety. Conversely, for the aboveexample, the fluid could be safely withdrawn from the patient at a lowerpressure (higher negative pressure) and still maintain the same marginof safety.

FIG. 4 is a block diagram illustrating the process of detecting therelative elevation and regulating fluid pump pressure according to oneembodiment of the present invention. In this embodiment, the fluid flowcontrol system of FIG. 2 is employed. The pressure of at least one ofthe pumps 300 and 310 are correlated with that of the pressure at thedistal end 208 of the fluid line 204, which, in turn may be related tothe elevation differential. The correlation is complicated due to thefact that, in membrane-based systems, the flexible membranes 303 and 313store some of the pV work as elastic energy resulting in slightlydifferent pressures across the membrane at equilibrium. Therefore, theinvention provides for measurements, correlation, and the development ofrelationships prior to measuring the relative elevation. Without suchcorrelation, the estimate of the relative elevation could be in error byas much as eight to ten inches. The inventors have discovered that newmembranes in such systems exhibit hysteresis. Such hysteresis appears todiminish as the membranes are repeatedly flexed. Therefore, thecalibration may be performed after other startup procedures that flexthe membrane are completed.

Referring to FIG. 2 for the various referenced items, the pressure in atleast one pump 300 or 310 is calibrated in process 401. In process 402,fluid communication is established between the at least one pump 300 or310 and the line 204. The static pressure in the pump in communicationwith the line is measured in process 403, and the relative elevationbetween the line and the fluid flow control device is estimated inprocess 404. This is accomplished by using the static pressure measuredin the pump and by using a known relationship between a heightdifferential and pressure differential (e.g., 0.3 m (1 foot) per 25 mmHg.) Finally, the pump pressure may be adjusted to accommodate theheight differential in process 405.

FIG. 5( a) shows a block diagram highlighting the start up andcalibration procedures according to a preferred embodiment of theinvention that employs the fluid flow control system of FIG. 2. Theliquid volumes 302 and 312 are emptied in process 501 since either oneor both volumes may be partially full from previous procedures. Afterboth liquid volumes 302 and 312 are emptied, both outlet valves 306 and316 are closed in process 502. Both liquid volumes 302 and 312 aregravity filled with fluid in process 503. In this embodiment, the fluidis obtained through an inlet line from heated solution bag 202 as shownin FIG. 1. Since the solution bag 202 sits on top of the fluid flowcontrol device 200, the static head resulting from the difference inelevation between the solution bag 202 and the pumps 300 and 310 isknown and small. Liquid volumes 302 and 312 are filled via gravity assolution bag 202 is located at a higher elevation than are liquidvolumes 302 and 312.

The pressures in the control volumes 301 and 311 are measured in process504 using the pressure transducers 305 and 315. A transducer may be anyinstrument for converting a pressure to a signal, preferably anelectrical signal. The pressures measured in process 504 are to becorrelated to a zero static head (or defined to be zero). Both pumpinlet valves 307 and 317 are closed and the occluder bar 205 isactivated in process 505. The order of closure and activation is notsignificant. The effect of process 505 is to isolate the fluid in theliquid volumes 302 and 312 and outlet line 204 upstream of the occluderbar 205. In process 506 both outlet valves 306 and 316 are opened.Opening both outlet valves 306 and 316 enables fluid to be pumpedbetween the two liquid volumes 302 and 312 while keeping the total fluidvolume within the liquid volumes 302 and 312 constant.

The first control volume 301 is pressurized in process 507 to apre-selected positive pressure. The selection of the pre-selectedpositive pressure is determined by factors such as the expected range ofrelative elevations and the dynamic range of the pressure transducers305 and 315. The pressure in the first control volume 301 simulates aknown static head. The pressure in the second control volume 311 ismeasured in process 508 by the pressure transducer 315.

By assuming that the two membranes are identical in their effect onpressure transmission, a relationship is derivable from the two sets ofpressure measurements, and calibration constants may be calculated atthis point. However, in further preferred embodiments of the invention,processes 507 and 508 are repeated. This time, the first control volume301 is pressurized using a pre-selected negative pressure in process 509and the pressure in the second control volume is measured in process510. In process 511 of this embodiment, a relationship is derived fromthe three sets of pressure measurements, and calibration constants arecalculated.

FIG. 5( b) is a block diagram illustrating the processes following thestart up and calibration procedures of FIG. 5( a). In process 512 theliquid volumes 302 and 312 are again gravity filled. The valved outletis adjusted in process 513 allowing fluid communication only between thesecond pump 310 and the outlet line 204. The adjustment is accomplishedby emptying the first control volume 301, closing the first outlet valve306, and deactivating the occluder bar 205. The result of these actionsplaces the second pump 310 in fluid communication with the outlet line204 while isolating the second pump 310 from the rest of the system. Inprocess 514, the pressure transducer 315 measures the pressure in thesecond control volume 311, and the relative elevation is estimated inprocess 515 based on the pressure in the second control volume and thecalibration constants generated during calibration.

FIG. 6 is a graphical representation of two piecewise linear fits usingcoordinates of relative elevation (on the ordinate) and the pressuremeasured in process 514, P(control volume) (on the abscissa). The headpressure may be determined from the relative elevation by the equationp=.rho.gh, where p is the pressure, .rho. is the fluid density, g is theacceleration due to gravity, and h is the relative elevation. A point, H(on the ordinate), is determined by erecting a perpendicular from theP(control volume) value on the abscissa to the linear fit derived fromthe six calibration pressure values. Subsequently, the pressure at thedistal end 208 of the fluid line 204, P(distal end), due to theelevation differential may be calculated in process 516. Finally, thepressure in the pumps 300 and 310 may be adjusted in process 517 toaccommodate the height differential.

A computer program product may be employed for implementing the methodsof the present invention. The computer program product comprises acomputer usable medium having computer readable program code thereon.The computer readable program may include program code for reading andstoring pressure values within the liquid volume 302 or 312, programcode for computing and identifying correlations between stored pressurevalues, program code for calculating pressure values based on theidentified correlations, and program code for estimating the elevationdifferential based upon the calculated pressures. The computer programproduct may also include program code for calculating a desired fluidpump pressure based upon the elevation differential and program code foradjusting the pump pressure in accordance with the desired pumppressure.

The computer program product may be run on a data processing unit, whichacts as a controller. Such a unit may be capable of adjusting the flowrate of fluid being pumped to the distal end 208 by adjusting the pumppressure. For example, if the calculation determined that the distal end208 of the fluid line 204 and the fluid control system were at the sameheight, the pump pressure might be safely increased above 75 mm Hgresulting in faster fluid flow rate. Further, all method processes maybe performed under processor control. A memory may be provided to storeupper limits on safe pressures at the distal end 208 of the line 204based upon the elevation differential between the distal end 208 and thesystem. A processor capable of receiving data as to elevationdifferential could then calculate and control pressure levels.

Although, in the system described herein above, the liquid volumes usedto determine the relative elevation are pumps containing membranes, itwill appreciated that separate pumps, control volumes, and liquidvolumes may be provided and that the liquid volumes and control volumesmay be located at a different point from the pumps along the fluidpathway to the distal end of the fluid line. In such an embodiment, theheight difference between the liquid volumes and the pumps or controlvolumes should be constant, so that the height difference is known. Itshould also be appreciated that the liquid volumes and the pressurizingmeans need not be at the same location, and that the first and secondliquid volumes may likewise be in separate locations.

It will be further understood by one of ordinary skill in the art thatother modifications can be made without departing from the spirit andthe scope of the invention, as set forth in the claims below.

What is claimed is:
 1. A method for regulating fluid pump pressures at adistal end of a solution line in a peritoneal dialysis system, theperitoneal dialysis system comprising a fluid flow control apparatushaving a membrane-based pump fluidly connected to the solution line, themethod comprising: establishing a desired pressure limit for fluidpressure at the distal end of the solution line; determining a staticpressure in the fluid flow control apparatus; establishing fluidcommunication between the fluid flow control apparatus and the solutionline; determining a static pressure at the distal end of the solutionline; calculating a pressure to be applied to a membrane-based fluidpump based on a pressure differential between a static pressure at thedistal end of the solution line and a static pressure in the fluid flowcontrol apparatus; and applying the pressure to the membrane-based pumpto achieve a pressure at the distal end of the solution line that doesnot exceed the desired pressure limit.
 2. The method of claim 1 whereinthe membrane-based pump comprises a flexible membrane.
 3. The method ofclaim 1 wherein the membrane-based pump is pressurized by utilizing acontrol fluid.
 4. The method of claim 3 wherein the control fluid is agas.
 5. The method of claim 1 wherein the membrane-based pump ispressurized by utilizing a piston.
 6. The method of claim 1 wherein thestep of calculating the pressure to be applied to the membrane-basedpump is also based on a desired flow rate of fluid to be pumped to thedistal end of the solution line.
 7. A method for regulating fluid pumppressures at a distal end of a solution line in an intravenous fluiddelivery system, the intravenous fluid delivery system comprising afluid flow control apparatus having a membrane-based fluid pump fluidlyconnected to the solution line, the method comprising: establishing adesired pressure limit for fluid pressure at the distal end of thesolution line; determining a static pressure in the fluid flow controlapparatus; establishing fluid communication between the fluid flowcontrol apparatus and the solution line; determining a static pressureat the distal end of the solution line; calculating a pressure to beapplied to the membrane-based fluid pump based on a pressuredifferential between a static pressure at the distal end of the solutionline and a static pressure in the fluid flow control apparatus; andapplying the pressure to the membrane-based fluid pump to achieve apressure at the distal end of the solution line that does not exceed thedesired pressure limit.
 8. The method of claim 7 wherein themembrane-based fluid pump comprises a flexible membrane.
 9. The methodof claim 7 wherein the membrane-based fluid pump is pressurized byutilizing a control fluid.
 10. The method of claim 9 wherein the controlfluid is a gas.
 11. The method of claim 7 wherein the membrane-basedfluid pump is pressurized by utilizing a piston.
 12. The method of claim7 wherein the step of calculating the pressure to be applied to themembrane-based fluid pump is also based on a desired flow rate of fluidto be pumped to the distal end of the solution line.
 13. A method forregulating fluid pump pressures at a distal end of a solution line influid flow control system, fluid flow control system comprising a fluidflow control apparatus having a membrane-based fluid pump fluidlyconnected to the solution line, the method comprising: establishing adesired pressure limit for fluid pressure at the distal end of thesolution line; determining a static pressure in the fluid flow controlapparatus; establishing fluid communication between the fluid flowcontrol apparatus and the solution line; determining a static pressureat the distal end of the solution line; calculating a pressure to beapplied to the membrane-based fluid pump based on a pressuredifferential between a static pressure at the distal end of the solutionline and a static pressure in the fluid flow control apparatus; applyingthe pressure to the membrane-based fluid pump to achieve a pressure atthe distal end of the solution line that does not exceed the desiredpressure limit.
 14. The method of claim 13 wherein the membrane-basedfluid pump comprises a flexible membrane.
 15. The method of claim 13wherein the membrane-based fluid pump is pressurized by utilizing acontrol fluid.
 16. The method of claim 15 wherein the control fluid is agas.
 17. The method of claim 13 wherein the membrane-based fluid pump ispressurized by utilizing a piston.
 18. The method of claim 13 whereinthe step of calculating the pressure to be applied to the membrane-basedfluid pump is also based on a desired flow rate of fluid to be pumped tothe distal end of the solution line.
 19. A method operating on a digitalcomputer system for regulating fluid pump pressures at a distal end of asolution line in a fluid flow control system, the fluid flow controlsystem comprising a fluid flow control apparatus having a membrane-basedpump fluidly connected to the solution line, the method comprising:storing a desired pressure limit for fluid pressure at the distal end ofthe solution line; receiving information corresponding to a staticpressure in the fluid flow control apparatus; permitting fluidcommunication to be established between the fluid flow control apparatusand the solution line; receiving information corresponding to a staticpressure at the distal end of the solution line; calculating a pressureto be applied to the membrane-based pump based on a pressuredifferential between a static pressure at the distal end of the solutionline and a static pressure in the fluid flow control apparatus; andsending a control signal to adjust the pressure to the membrane-basedpump to achieve a pressure at the distal end of the solution line thatdoes not exceed the desired pressure limit.
 20. The method of claim 19,wherein the fluid flow control system comprises a peritoneal dialysissystem.
 21. The method of claim 19, wherein the fluid flow controlsystem comprises an intravenous fluid delivery system.
 22. Acomputer-readable medium having a computer program stored thereon andconfigured to cause a controller to regulate fluid pump pressures at adistal end of a solution line in a fluid flow control system, the fluidflow control system comprising a fluid flow control apparatus having amembrane-based pump fluidly connected to the solution line, the computerprogram configured to cause the controller to: store a desired pressurelimit for fluid pressure at the distal end of the solution line; receiveinformation corresponding to a static pressure in the fluid flow controlapparatus; permit fluid communication to be established between thefluid flow control apparatus and the solution line; receive informationcorresponding to a static pressure at the distal end of the solutionline; calculate a pressure to be applied to the membrane-based fluidpump based on a pressure differential between a static pressure at thedistal end of the solution line and a static pressure in the fluid flowcontrol apparatus; and send a control signal to adjust the pressure tothe membrane-based pump to achieve a pressure at the distal end of thesolution line that does not exceed the desired pressure limit.
 23. Thecomputer-readable medium of claim 22, wherein the fluid flow controlsystem comprises a peritoneal dialysis system.
 24. The computer-readablemedium of claim 22, wherein the fluid flow control system comprises anintravenous fluid delivery system.